motility

In biology, motility is the ability of organisms and fluid to move or get around. A microbiologist might test and compare the motility of various single-celled organisms.

An easy way to remember that motility means the ability to move without help is the mot- at the root of the word. It's the same root that's found in "motor," which is, of course, the engine that drives a car. If you've got good motility then your motor is working. After a car accident accident, an athlete's friends are understandably concerned about her motility. Motility is something you tend to take for granted — until you sprain an ankle.